Cartilage

Question 1

What common structures are composed of fibrocartilage

Answer 1

• Illiac surface of SI joints
• Menisci of the knee
• annular fibers of the disks

Question 2

Components of cartilage and function of cartilage

Answer 2

Function:

• Decrease contact stress on articular surfaces by spreading load over larger area
• Allow movement of articular surfaces with minimal wear and friction

Components:
-Solid matrix: proteoglycan gel (20-40% weight)
Collagen 60% weight
-Chondrocytes (over 2% of solid matrix)
-Water (60-80% of total weight)

Question 3

Why it is appropriate that collagen in cartilage is better suited to resist tensile loads rather
than compressive loads.

Answer 3

The superficial zone 40-60% of thickness has the collagen arrangement in planes parallel to the surface

Question 4

Syringe effect

Answer 4

An increase in stiffness when a load is applied with increased speed.
Involved with high speed loading:
-insufficient time to squeeze water out of tissue
-the cartilage thus is very stiff
-there is little deformation

Question 5

Aggrecans, how they help to establish the sponge model, the details of how water moves
to protect the joints.

Answer 5

Aggrecans is a component of proteoglycan gel
- aggrecans are composed of chondritin sulfate and keratan sulfate

-Strong repulsive force between anions stiffens the PG gel to resist compression
-cloud of cations are attracted to negative charges
-the cloud of ions osmotically draw water molecules into cartilage
the charge of the PG gel attracts positive ions and sets up an osmotic pressure

• the cartilage stiffens and swells due to the repulsive force of the aggrecans, osmotic pressure forms attracting water

Question 6

The characteristics of creep as it applies to cartilage.

Answer 6

• under a constant load a viscoelastic material will deform quickly at first then more slowly over time

Question 7

How the speed of loading affects the material behaviour of cartilage

Answer 7

• High speed loading: syringe effect
• increasing the speed of loading causes the cartilage to appear stiff

Unloading slowly results in immediate restoration 90% original thickness via elastic recoil

Question 8

Fluid film (hydrodynamic and squeeze) vs boundary lubrication

Answer 8

Fluid film lubrication is a thick film of lubricant separates the surfaces
-occurs in physiologic loading
two types:
Hydrodynamic- non parallel surfaces, tangential movement, creates lifting action
Squeeze film- surfaces are kept apart, perpendicular force, viscosity holds lubricant together, sufficient for high loads for short durations

Boundary Lubrication: important in severe loading a monolayer of synovial fluid that absorbs to surfaces

Question 9

Interfacial wear vs fatigue wear

Answer 9

Interfacial wear
-From interaction of articular surfaces, by adhesion and abrasion, unlikely in healthy cartilage, wear produces surface defect, fluid leakage, loss of lubrication

Fatigue wear

• occurs with repetitive cyclic loading
• reloading occurs before cartilage has time to reimbibe
• repetitive stress on matrix

Question 10

Types of factors/occupations/disease that lead to cartilage injury

Answer 10

High repetitive loads
Loss of muscle balance
Defect that focuses load into one area
Joint space haemorrhage
Immobility
Degeneration